This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2001-173056 filed on Jun. 7, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
This invention generally relates to a system for detecting a sensor error. More particularly, the present invention pertains to a system for detecting a sensor error of such as an acceleration sensor and an angular velocity sensor used for detecting such as longitudinal acceleration of a vehicle and yaw rate.
2. Background of the Invention
Japanese Patent Laid-Open Publication No. H07-83951 discloses an angular velocity sensor having a self-diagnosis feature. This angular velocity sensor includes a detecting element portion, a signal processing circuit portion for processing output from the detecting element portion, and an electromagnetic generating portion provided close to the detecting element portion for activating the detecting element portion. In the disclosed angular sensor, the error is detected by checking the output from the signal processing circuit portion produced by activating the detecting element portion by the electromagnetic generating portion to provide a pseudo Coriolis force to the element under the condition that no angular velocity is inputted to the detecting element portion. In this angular velocity sensor, if an output producing portion of a pseudo detecting element portion, which produces the output from the pseudo detecting element portion being inputted to the signal processing circuit portion, is provided instead of the electromagnetic generating portion, the error in the signal processing circuit portion can be detected though the error in the detecting element portion cannot be detected.
In the system disclosed in the Japanese Patent Laid-Open Publication No. H07-83951, the output from the signal processing circuit portion is checked only when the detecting element portion is activated by the electromagnetic generating portion. Accordingly, if the angular velocity is actually inputted while the self-diagnosis is executed, the sensor error can be determined even though no errors exist in the angular velocity sensor, which leads to the dissatisfaction with the detecting accuracy.
It is an object of the present invention to provide a higher accuracy for detecting a sensor error.
According to the present invention, the system for detecting the sensor error includes a sensor having a detecting portion and a signal processing portion, and the error is detected in this system based on a signal outputted from the signal processing portion by performing a pseudo drive either by providing a pseudo external input to the detecting portion or by providing a pseudo detecting portion output signal to the signal processing portion under the condition that an external input is not inputted to the detecting portion. In this system, firstly, an average value of the signal outputted from the signal processing portion within a first predetermined time from a start to an end of the pseudo drive, an average value of the signal outputted from the signal processing portion within a second predetermined time before the start of the pseudo drive, and an average value of the signal outputted from the signal processing portion within a third predetermined time after the end of the pseudo drive are evaluated. Then, if a difference between a value evaluated by prorating a sum of the above average value of the signal outputted from the signal processing portion within the second predetermined time before the start of the pseudo drive and the above average value of the signal outputted from the signal processing portion within the third predetermined time after the end of the pseudo drive, and the above average value of the signal outputted from the signal processing portion within the first predetermined time from the start to the end of the pseudo drive does not fall within a predetermined value, then the sensor error is determined.
Accordingly, in this invention, the sensor error is determined if the difference between the value evaluated by prorating the sum of the average value outputted from the signal processing portion within the second predetermined time before the start of the pseudo drive and the average value outputted from the signal processing portion within the third predetermined time after the end of the pseudo drive, and the average value outputted from the signal processing portion within the first predetermined time from the start to the end of the pseudo drive does not fall within the predetermined value. Then, if the external input is actually inputted under the condition that the external input to the detecting portion is not supposed to be inputted, the influence of the external input appears on the output from the signal processing portion before and after the pseudo drive. Accordingly, by determining the sensor error based on the output from the signal processing portion during the pseudo drive and before and after thereof, the detecting accuracy is more improved.
In this invention, if each fluctuation of the signal outputted from the signal processing portion from the start to the end of the pseudo drive, the signal outputted from the signal processing portion within the second predetermined time before the start of the pseudo drive, and the signal outputted from the signal processing portion within the third predetermined time after the end of the pseudo drive does not fall within a predetermined fluctuation range, and/or, a deviation of the average value of the signal outputted from the signal processing portion within the second predetermined time before the start of the pseudo drive from the average value of the signal outputted from the signal processing portion within the third predetermined time after the end of the pseudo drive is greater than a predetermined value, the error determination may not be performed. In this case, the predetermined fluctuation range is set so that the fluctuation of the output from the signal processing portion goes beyond the predetermined range if the external input is inputted under the normal sensor condition. The fluctuation range is experimentally evaluated. Also the predetermined value is set so that the above-mentioned deviation cannot exceed the predetermined value due to the normal sensor characteristic change caused by the pseudo drive under the normal sensor condition. The predetermined value is also experimentally evaluated.